DatabaseCacheTagsChecksum::calculateChecksum

protected DatabaseCacheTagsChecksum::calculateChecksum(array $tags)

protected function calculateChecksum(array $tags) {
  $checksum = 0;

  $query_tags = array_diff($tags, array_keys($this->tagCache));
  if ($query_tags) {
    $db_tags = array();
    try {
      $db_tags = $this->connection->query('SELECT tag, invalidations FROM {cachetags} WHERE tag IN ( :tags[] )', array(':tags[]' => $query_tags))
        ->fetchAllKeyed();
      $this->tagCache += $db_tags;
    }
    catch (\Exception $e) {
      // If the table does not exist yet, create.
      if (!$this->ensureTableExists()) {
        $this->catchException($e);
      }
    }
    // Fill static cache with empty objects for tags not found in the database.
    $this->tagCache += array_fill_keys(array_diff($query_tags, array_keys($db_tags)), 0);
  }

  foreach ($tags as $tag) {
    $checksum += $this->tagCache[$tag];
  }

  return $checksum;
}